New Recipe for Dwarf Galaxies: Start with Leftover Gas

NASA's Galaxy Evolution Explorer reveals, for the first time, dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe. Credit: NASA/JPL-Caltech/DSS


Apparently, dwarf galaxies can spring out of thin air.

Astronomers using NASA’s Galaxy Evolution Explorer have spotted unexpected new galaxies in the constellation Leo that appear to be forming out of nothing more than pristine gas, probably leftover from the early universe.  The gas lacks both dark matter and metals — previously thought to be building blocks for galaxy formation.

Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way. Though never seen before, the researchers say this new type of dwarf galaxy may be common throughout the more distant and early universe, when pristine gas was more pervasive. Their discovery appears in this week’s issue of the journal Nature.

The newly described dwarf galaxies are in the Leo Ring, a huge cloud of hydrogen and helium that traces a ragged path around two massive galaxies in the constellation Leo. The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe. Identified about 25 years ago by radio waves, the ring cannot be seen in visible light.

“This intriguing object has been studied for decades with world-class telescopes operating at radio and optical wavelengths,” said lead study author David Thilker of Johns Hopkins University in Baltimore. He added that no stars were ever seen in the gaseous regions before. 

“But when we looked at the ring with the Galaxy Evolution Explorer, which is remarkably sensitive to ultraviolet light, we saw telltale evidence of recent massive star formation. It was really unexpected. We are witnessing galaxies forming out of a cloud of primordial gas.”

Our local universe contains two large galaxies, the Milky Way and the Andromeda galaxy, each with hundreds of billions of stars, and the Triangulum galaxy, with several tens of billions of stars. It also holds more than 40 much smaller dwarf galaxies, which have only a few billion stars. Invisible dark matter, detected by its gravitational influence, is a major component of both giant and dwarf galaxies with one exception — tidal dwarf galaxies.

Tidal dwarf galaxies condense out of gas recycled from other galaxies and have been separated from most of the dark matter with which they were originally associated. They are produced when galaxies collide and their gravitational masses interact. In the violence of the encounter, streamers of galactic material are pulled out away from the parent galaxies and the halos of dark matter that surround them.

Because they lack dark matter, the new galaxies observed in the Leo Ring resemble tidal dwarf galaxies, but they differ in a fundamental way. The gaseous material making up tidal dwarfs has already been cycled through a galaxy. It has been enriched with metals — elements heavier than helium — produced as stars evolve. “Leo Ring dwarfs are made of much more pristine material without metals,” Thilker said. “This discovery allows us to study the star formation process in gas that has not yet been enriched.”

Large, pristine clouds similar to the Leo Ring may have been more common throughout the early universe, Thilker said, and consequently may have produced many dwarf galaxies yet to be discovered that also lack dark matter.

Source: Caltech

The forming dwarf galaxies shine in the far ultraviolet spectrum, rendered as blue in the call-out on the right hand side of this image. Near ultraviolet light, also obtained by the Galaxy Evolution Explorer, is displayed in green, and visible light from the blue part of the spectrum here is represented by red. The clumps (in circles) are distinctively blue, indicating they are primarily detected in far ultraviolet light. The faint blue overlay traces the outline of the Leo Ring, a huge cloud of hydrogen and helium that orbits around two massive galaxies in the constellation Leo (left panel). Credit: NASA/JPL-Caltech/DSS

Galaxy Zoo 2 Launches

Galaxy Zoo.


Do you Zoo? Well, now you can Zoo 2. Galaxy Zoo, that is. Galaxy Zoo 2 is a new version of the highly successful project that enables members of the public to take part in astronomy research online. But the research is now getting more interesting, and shall we say, more provocative? The original site only asked members of the public to say whether a galaxy was spiral or elliptical, and which way it was rotating, Galaxy Zoo 2 asks users to delve deeper into 250,000 of the brightest and best galaxies to search for the strange and unusual. “We we were so surprised about how many people participated in Galaxy Zoo and how good they were at this,” said Dr. Chris Lintott of Oxford University, one of the founders of Galaxy Zoo. “But now the idea is to ask for more detailed classifications. So it’s a Faustian pact we’re making with our users. We want them to spend more time with each galaxy, so it’s not just this fly by night, quick one-night stand of galaxy classification. We want them to get to know each galaxy a little bit better, have dinner first and all of that. But as a compromise, we have only a quarter of a million of the most interesting galaxies, the brightest, and the nearest. So you’ll spend more time looking at galaxies, but they’re prettier.”

At latest count, Galaxy Zoo has 182,383 users, (which Lintott notes is more people than live in Guam or Sunderland) who have performed 74,503,984 classifications of galaxies.

Lintott told Universe Today that Galaxy Zoo is a classic pub idea that worked. “I was working with Kevin Schawinski of Yale University on galaxies,” he said, and to get accurate data, they needed to classify a large number of galaxies. “We’d heard about Stardust at Home, which is an amazing project. I was impressed they were able to do this, to get people search for dust grains. And we’ve got all these pretty pictures of galaxies to look at, so surely people would like to look at galaxies. We put the site together, and we’ve been overwhelmed with the response.”

Galaxies from Galaxy Zoo.
Galaxies from Galaxy Zoo.

The human eye and brain are better at doing pattern recognition tasks than a computer. Lintott noted that astronomers have spent 70 years classifying galaxies according the laws that Hubble put down, but only by classifying a really large number are astronomers going to have any sense of what the population of different types of galaxies are.

“Is there really any difference between and Sa and an Sb galaxy?” asked Lintott. “They’re defined by different tightnesses of spiral arms and different bulge shapes, but we want to know, do they live in the same place or do they have the same star formation histories or what is going on with the black holes? So we need to classify many galaxies into these categories. So that’s the idea for Zoo 2. Rather than getting people to remember the categories we have a series of questions that you go through so we get individual information about the galaxies.”

As with the original site people are free to look at and describe as many galaxies as they like – even five minutes’ work will provide a valuable contribution. Galaxy Zoo 2 is intended to be even more fun as galaxies are pitted against each other in “Galaxy Wars” (which one is more spirally?) and users can compete against their friends to describe more objects as well as record their best finds.

Zoo 2 has been in a test phase for a couple of months, and everything seems to be working well, as hundreds of thousands of classifications have already been done in the new version. “There was a worry that maybe we had exhausted people’s tolerance for galaxies, but apparently not,” said Lintott.

To join in on the fun, check out Galaxy Zoo.

The BBC talked with Chris Lintott, too, and they have a nice video overview of Galaxy Zoo and Zoo 2.

Source: Interview with Chris Lintott.

Ultra Compact Dwarf Galaxies once crowded with stars

The background image was taken by Michael Hilker of the University of Bonn using the 2.5-metre Du Pont telescope, part of the Las Campanas Observatory in Chile. The two boxes show close-ups of two UCD galaxies in the Hilker image. These images were made using the Hubble Space Telescope by a team led by Michael Drinkwater, at the University of Queensland

Astronomers think they’ve found a way to explain why Ultra Compact Dwarf Galaxies, oddball creations from the early universe, contain so much more mass than their luminosity would explain.

Pavel Kroupa, an astronomer at the University of Bonn in Germany, led a research team that’s proposing the unexplained density may actually be a relic of stars that were once packed together a million times more closely than in the solar neighbourhood. The new paper appears in the Monthly Notices of the Royal Astronomical Society.

UCDs were discovered in 1999. At about 60 light years across, they are less than 1/1000th the diameter of the Milky Way — but much more dense. Astronomers have proposed they formed billions of years ago from collisions between normal galaxies. Until now, exotic dark matter has been suggested to explain the ‘missing mass.’

The authors of the new study think that at one time, each UCD had an incredibly high density of stars, with perhaps 1 million in each cubic light year of space, compared with the 1 that we see in the region of space around the Sun. These stars would have been close enough to merge from time to time, creating many much more massive stars in their place. The more massive stars would consume hydrogen rapidly, before ending their lives in violent supernova explosions, leaving either superdense neutron stars or black holes as their remains. 

In today’s UCDs, the authors think, the previously unexplained mass comprises these dark remnants, largely invisible to Earth-based telescopes.

“Billions of years ago, UCDs must have been extraordinary,” study co-author Joerg Dabringhausen, also of the University of Bonn, said in a press release. “To have such a vast number of stars packed closely together is quite unlike anything we see today. An observer on a (hypothetical) planet inside a UCD would have seen a night sky as bright as day on Earth.”

PHOTO CAPTION: Background image taken by Michael Hilker of the University of Bonn using the 2.5-metre Du Pont telescope, part of the Las Campanas Observatory in Chile. The two boxes show close-ups of two UCD galaxies in the Hilker image. These images were made using the Hubble Space Telescope by a team led by Michael Drinkwater, at the University of Queensland.

Source: Royal Astronomical Society

Next-Generation Telescope Gets Team

Artist's rendering of the Giant Magellan Telescope and support facilities at Las Campanas Observatory, Chile, high in the Andes Mountains. Photo by Todd Mason/Mason Productions



Astronomy organizations in the United States, Australia and Korea have signed on to build the largest ground-based telescope in the world – unless another team gets there first. The Giant Magellan Telescope, or GMT, will have the resolving power of a single 24.5-meter (80-foot) primary mirror, which will make it three times more powerful than any of the Earth’s existing ground-based optical telescopes. Its domestic partners include the Carnegie Institution for Science, Harvard University, the Smithsonian Institution, Texas A & M University, the University of Arizona, and the University of Texas at Austin. Although the telescope has been in the works since 2003, the formal collaboration was announced Friday.

Charles Alcock, director of the Harvard-Smithsonian Center for Astrophysics, said the Giant Magellan Telescope is being designed to build on the legacy of a rash of smaller telescopes from the 1990s in California, Hawaii and Arizona. The existing telescopes have mirrors in the range of six to 10 meters (18 to 32 feet), and – while they’re making great headway in the nearby universe – they’re only able to make out the largest planets around other stars and the most luminous distant galaxies.

With a much larger primary mirror, the GMT will be able to detect much smaller and fainter objects in the sky, opening a window to the most distant, and therefore the oldest, stars and galaxies. Formed within the first billion years of the Big Bang, such objects reveal tantalizing insight into the universe’s infancy.

Earlier this year, a different consortium including the California Institute of Technology and the University of California, with Canadian and Japanese institutions, unveiled its own next-generation concept: the Thirty Meter Telescope. Whereas the GMT’s 24.5-meter primary mirror will come from a collection of eight smaller mirrors, the TMT will combine 492 segments to achieve the power of a single 30-meter (98-foot) mirror design.

In addition, the European Extremely Large Telescope is in the concept stage.

In terms of science, Alcock acknowledged that the two telescopes with US participation are headed toward redundancy. The main differences, he said, are in the engineering arena.

“They’ll probably both work,” he said. But Alcock thinks the GMT is most exciting from a technological point of view. Each of the GMT’s seven 8.4-meter primary segments will weigh 20 tons, and the telescope enclosure has a height of about 200 feet. The GMT partners aim to complete their detailed design within two years.

The TMT’s segmented concept builds on technology pioneered at the W.M. Keck Observatory in Hawaii, a past project of the Cal-Tech and University of California partnership.

Construction on the GMT is expected to begin in 2012 and completed in 2019, at Las Campanas Observatory in the Andes Mountains of Chile. The total cost is projected to be $700 million, with $130 million raised so far. 

Artists concept of the Thirty Meter Telescope Observatory. Credit: TMT
Artists concept of the Thirty Meter Telescope Observatory. Credit: TMT

Construction on the TMT could begin as early as 2011 with an estimated completion date of 2018. The telescope could go to Hawaii or Chile, and final site selection will be announced this summer. The total cost is estimated to be as high as $1 billion, with $300 million raised at last count.


Alcock said the next generation of telescopes is crucial for forward progress in 21st Century astronomy.

“The goal is to start discovering and characterizing planets that might harbor life,” he said. “It’s very clear that we’re going to need the next generation of telescopes to do that.”

And far from being a competition, the real race is to contribute to science, said Charles Blue, a TMT spokesman.

“All next generation observatories would really like to be up and running as soon as possible to meet the scientific demand,” he said.

In the shorter term, long distance space studies will get help from the James Webb Space Telescope, designed to replace the Hubble Space Telescope when it launches in 2013. And the Atacama Large Millimeter Array (ALMA), a large interferometer being completed in Chile, could join the fore by 2012.

Sources: EurekAlert and interviews with Charles Alcock, Charles Blue

Deep Hubble View of Unusual “Fluffy” Galaxy – and Beyond

This deep image taken with the NASA/ESA Hubble Space Telescope shows the spiral galaxy NGC 4921 along with a spectacular backdrop of more distant galaxies. It was created from a total of 80 separate pictures taken with yellow and near-infrared filters. Credits: NASA, ESA and K. Cook (Lawrence Livermore National Laboratory, USA)


The Coma Galaxy cluster is home to a rich collection of galaxies in the nearby Universe. NGC 4921 is one of the rare spirals in Coma, and a rather unusual one. It looks “fluffy,” with lots of swirling dust. Astronomers say this galaxy is an “anemic spiral” where a small amount of star formation is taking place, and so less light is coming from the galaxy’s arms, as is usually seen in a spiral galaxy. This is an image from the Hubble Space Telescope, and with Hubble’s sharp vision, you can see a few bright young blue stars. But what’s really amazing, besides seeing the incredible detail of NGC 4921, is looking beyond the big fluffy galaxy and seeing how Hubble was able to pick up a marvelous collection of remote galaxies of all shapes, sizes and colors. Many have the spotty and ragged appearance of galaxies from the early Universe. Click here to get a bigger, better view.

This image was created from data obtained by Hubble’s Advanced Camera for Surveys. The Coma galaxy cluster, is in the northern constellation of Coma Berenices. The cluster, also known as Abell 1656, is about 320 million light-years from Earth and contains more than 1000 members. The brightest galaxies, including NGC 4921, were discovered back in the late 18th century by William Herschel.

Annotated deep Hubble Space Telescope image of NGC 4921 indictating the locations of some of the more interesting features of the galaxy and its surroundings.   Credits: NASA, ESA and K. Cook (Lawrence Livermore National Laboratory, USA)
Annotated deep Hubble Space Telescope image of NGC 4921 indictating the locations of some of the more interesting features of the galaxy and its surroundings. Credits: NASA, ESA and K. Cook (Lawrence Livermore National Laboratory, USA)

The galaxies in rich clusters undergo many interactions and mergers that tend to gradually turn gas-rich spirals into elliptical systems without much active star formation. As a result, there are far more ellipticals and fewer spirals in the Coma Cluster than are found in quieter corners of the Universe.

The Hubble images used to make this picture were originally obtained by a team led by Kem Cook (Lawrence Livermore National Laboratory, California). The team used Hubble to search for Cepheid variable stars in NGC 4921 that could be used to measure the distance to the Coma cluster and hence the expansion rate of the Universe.

Unfortunately the failure of the Advanced Camera for Surveys in early 2007 meant that they had insufficient data to complete their original program, although they hope to continue after the servicing mission. Very deep imaging data like this, which is available to anyone from the Hubble archives, may also be used for other interesting scientific exploration of this galaxy and its surroundings.

A wide-field image of the region around the Coma galaxy cluster (Abell 1656) constructed from the images in the Digitized Sky Survey. NGC 4921 is the largest galaxy to the left, and slightly below, the pair of galaxies at the centre of the image. The field-of-view is approximately 2.7 x 2.85 degrees.   Credits: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)
A wide-field image of the region around the Coma galaxy cluster (Abell 1656) constructed from the images in the Digitized Sky Survey. NGC 4921 is the largest galaxy to the left, and slightly below, the pair of galaxies at the centre of the image. The field-of-view is approximately 2.7 x 2.85 degrees. Credits: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)

The top image was created from 50 separate exposures with a yellow filter and another 30 exposures with a near-infrared filter using the Wide Field Channel of the Advanced Camera for Surveys on Hubble. The total exposure times were approximately 17 hours and 10 hours respectively.

Source: ESA

A Disturbance in the Force in Centaurus A

Centaurus A. Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)


There are some interesting dynamics going on with Centaurus A, an elliptical galaxy about 13 million light-years away. This is a very active and luminous region of space and a great disturbance is going on as another spiral galaxy is trying to get in on the action by merging with Centaurus A. But astronomers now have new insight on what causing all the ruckus: a supermassive black hole at the core of Centaurus A. Jets and lobes emanating from the central black hole have been imaged at submillimeter wavelengths for the first time by using the 12-meter Atacama Pathfinder Experiment (APEX) telescope in Chile. By using a combination of visible and X-ray wavelengths, astronomers were able to produce this striking new image. Help me APEX, you are our only hope!

Centaurus A (NGC 5128) is one of our closest galactic neighbors, and is located in the southern constellation of Centaurus. The supermassive black hole is the source of the force: strong radio and X-ray emissions. Visible in the image is a dust ring encircling the giant galaxy, and the fast-moving radio jets ejected from the galaxy center. In submillimeter light, the heat glow from the central dust disc can be seen and also the emission from the central radio source.

APEX was also able to discern – for the first time in the submillimeter – the inner radio lobes north and south of the disc. Measurements of this emission, which occurs when fast-moving electrons spiral around the lines of a magnetic field, reveal that the material in the jet is travelling at approximately half the speed of light. In the X-ray emission, we see the jets emerging from the centre of Centaurus A and, to the lower right of the galaxy, the glow where the expanding lobe collides with the surrounding gas, creating a shockwave.

Related paper.

Source: ESO

Zoom 13 Million Light-years to See Heart of Active Galaxy

Galaxy NGC 253 is shown here as observed with the WFI instrument, while the insert shows a close-up of the central parts as observed with the NACO instrument on ESO's Very Large Telescope and the ACS on the NASA/ESA Hubble Space Telescope. Credit: ESO

Using data from the Very Large Telescope’s powerful near-infrared eyes, astronomers have created a movie that takes you across 13 million light-years to galaxy NGC 253, an active galaxy filled with young, massive and dusty stellar nurseries. “We now think that these are probably very active nurseries that contain many stars bursting from their dusty cocoons,” says Jose Antonio Acosta-Pulido, a member of the team from Instituto de Astrofísica de Canarias in Spain. NGC 253 is known as a starburst galaxy, after its very intense star formation activity. Each bright region could contain as many as one hundred thousand young, massive stars. And in the center of this galaxy appears a strikingly familiar sight: a virtual twin of our own Milky Way’s supermassive black hole.

Watch the movie. (For different viewing options, click here).

The astronomers used NACO, a sharp-eyed adaptive optics instrument on the VLT to study the fine detail in NGC 253, one of the brightest and dustiest spiral galaxies in the sky. Adaptive Optics (AO) corrects for the blurring effect introduced by the Earth’s atmosphere. This turbulence causes the stars to twinkle in a way that delights poets, but frustrates astronomers, since it smears out the images. With AO in action the telescope can produce images that are as sharp as is theoretically possible, as if the telescope were in space.

NACO revealed features in the galaxy that were only 11 light-years across. “Our observations provide us with so much spatially resolved detail that we can, for the first time, compare them with the finest radio maps for this galaxy — maps that have existed for more than a decade,” says Juan Antonio Fernández-Ontiveros, the lead author of the paper reporting the results.

Close-up of the central regions of the starburst galaxy NGC 253.  Credit:  ESO
Close-up of the central regions of the starburst galaxy NGC 253. Credit: ESO

Astronomers identified 37 distinct bright regions packed into a tiny region at the core of the galaxy, comprising just one percent of the galaxy’s total size. This is three times more than seen previously. The astronomers combined their NACO images with data from the infrared instrument on VLT, the VISIR, as well as with images from the NASA/ESA Hubble Space Telescope and radio observations made by the Very Large Array and the Very Large Baseline Interferometer. Combining these observations, taken in different wavelength regimes, provided a clue to the nature of these regions.

In looking at all the data together, astronomers concluded that the center of NGC 253 hosts a scaled-up version of Sagittarius A*, the bright radio source that lies at the core of the Milky Way and which we know harbors a massive black hole. “We have thus discovered what could be a twin of our Galaxy’s Centre,” says co-author Almudena Prieto.

Source: ESO

Which Comes First: Galaxy or Black Hole?

Enlarge VLA image (right) of gas in young galaxy seen as it was when the Universe was only 870 million years old. Image: NRAO/AUI/NSF, SDSS


Do galaxies form first and then a black hole springs up in the center, or possibly, do galaxies form around an already existing black hole? That’s the cosmic chicken-and-the-egg problem astronomers have been trying to figure out. The answer? “It looks like the black holes form before the host galaxy, and somehow grow a galaxy around them. The evidence is piling up,” said Chris Carilli, of the National Radio Astronomy Observatory (NRAO), speaking at today’s press conference at the American Astronomical Society’s meeting. By observing with the Very Large Array radio telescope and the Plateau de Bure Interferometer in France at sub-kiloparsec resolution, the researchers have been “weighing” the earliest galaxies, ones that formed within a billion years of the Big Bang.

Previous studies of galaxies and their central black holes in the nearby Universe revealed an intriguing connection between the masses of the black holes and of the central “bulges” of stars and gas in the galaxies. The ratio of the black hole and the bulge mass is nearly the same for a wide range of galactic sizes and ages. For central black holes from a few million to many billions of times the mass of our Sun, the black hole’s mass is about one one-thousandth of the mass of the surrounding galactic bulge.

“This constant ratio indicates that the black hole and the bulge affect each others’ growth in some sort of interactive relationship,” said Dominik Riechers, of Caltech. “The big question has been whether one grows before the other or if they grow together, maintaining their mass ratio throughout the entire process.”

“We finally have been able to measure black-hole and bulge masses in several galaxies seen as they were in the first billion years after the Big Bang, and the evidence suggests that the constant ratio seen nearby may not hold in the early Universe. The black holes in these young galaxies are much more massive compared to the bulges than those seen in the nearby Universe,” said Fabian Walter of the Max-Planck Institute for Radioastronomy (MPIfR) in Germany.

“The implication is that the black holes started growing first.”

The next challenge is to figure out how the black hole and the bulge affect each others’ growth. “We don’t know what mechanism is at work here, and why, at some point in the process, the ‘standard’ ratio between the masses is established,” Riechers said.

New telescopes now under construction will be key tools for unraveling this mystery, Carilli explained. “The Expanded Very Large Array (EVLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) will give us dramatic improvements in sensitivity and the resolving power to image the gas in these galaxies on the small scales required to make detailed studies of their dynamics,” he said.

“To understand how the Universe got to be the way it is today, we must understand how the first stars and galaxies were formed when the Universe was young. With the new observatories we’ll have in the next few years, we’ll have the opportunity to learn important details from the era when the Universe was only a toddler compared to today’s adult,” Carilli said.

Carilli, Riechers and Walter worked with Frank Bertoldi of Bonn University; Karl Menten of MPIfR; and Pierre Cox and Roberto Neri of the Insitute for Millimeter Radio Astronomy (IRAM) in France.

Source: NRAO, AAS Press Conference

With No Smoke or Mirrors, Spacecraft Hunts for Active Galaxies with Central Black Holes

Swift's Hard X-ray Survey offers the first unbiased census of active galactic nuclei in decades. Dense clouds of dust and gas, illustrated here, can obscure less energetic radiation from an active galaxy's central black hole. High-energy X-rays, however, easily pass through. Credit: ESA/NASA/AVO/Paolo Padovani

NASA’s Swift spacecraft is designed to hunt for gamma-ray bursts. But in the time between these almost-daily cosmic explosions, Swift’s Burst Alert Telescope (BAT) scans the sky, performing an ongoing X-ray survey. Some of the first results of that survey were shared at the American Astronomical Society meeting in Long Beach, California. The BAT is revealing differences between nearby active galaxies and those located about halfway across the universe. Understanding these differences will help clarify the relationship between a galaxy and its central black hole. But unlike most telescopes, the BAT observations are not done with mirrors, optics or direct focusing. Instead, images are made by analyzing the shadows cast by 52,000 randomly placed lead tiles on 32,000 hard X-ray detectors. And BAT is becoming a workhorse: The survey is now the largest and most sensitive census of the high-energy X-ray sky.

“There’s a lot we don’t know about the workings of supermassive black holes,” says Richard Mushotzky of NASA’s Goddard Space Flight Center in Greenbelt, Md. Astronomers think the intense emission from the centers, or nuclei, of active galaxies arises near a central black hole containing more than a million times the sun’s mass. “Some of these feeding black holes are the most luminous objects in the universe. Yet we don’t know why the massive black hole in our own galaxy and similar objects are so dim.”

“The BAT sees about half of the entire sky every day,” Mushotzky said. “Now we have cumulative exposures for most of the sky that exceed 10 weeks.”
A beautiful "blue and booming" spiral galaxy sparkles with the light of rich clusters containing hot, young, massive stars. The blue color indicates the galaxy has a healthy "pulse" of star formation. The galaxy was imaged using the 2m telescope at Kitt Peak. Credit: NASA/Swift/NOAO/Michael Koss (Univ. of Maryland) and Richard Mushotzky
Galaxies that are actively forming stars have a distinctly bluish color (“new and blue”), while those not doing so appear quite red (“red and dead”). Nearly a decade ago, surveys with NASA’s Chandra X-Ray Observatory and ESA’s XMM-Newton showed that active galaxies some 7 billion light-years away were mostly massive “red and dead” galaxies in normal environments.

The BAT survey looks much closer to home, within about 600 million light-years. There, the colors of active galaxies fall midway between blue and red. Most are spiral and irregular galaxies of normal mass, and more than 30 percent are colliding. “This is roughly in line with theories that mergers shake up a galaxy and ‘feed the beast’ by allowing fresh gas to fall toward the black hole,” Mushotzky says.
This image shows a typical "red and dead" galaxy as seen by the Kitt Peak 2m telescope. The galaxy shows no sign of active star formation. Its color reddens as existing stars age. Credit: NASA/Swift/NOAO/Michael Koss (Univ. of Maryland) and Richard Mushotzky
Until the BAT survey, astronomers could never be sure they were seeing most of the active galactic nuclei. An active galaxy’s core is often obscured by thick clouds of dust and gas that block ultraviolet, optical and low-energy (“soft”) X-ray light. Dust near the central black hole may be visible in the infrared, but so are the galaxy’s star-formation regions. And seeing the black hole’s radiation through dust it has heated gives us a view that is one step removed from the central engine. “We’re often looking through a lot of junk,” Mushotzky says.

But “hard” X-rays — those with energies between 14,000 and 195,000 electron volts — can penetrate the galactic junk and allow a clear view. Dental X-rays work in this energy range.

Astronomers think that all big galaxies have a massive central black hole, but less than 10 percent of these are active today. Active galaxies are thought to be responsible for about 20 percent of all energy radiated over the life of the universe, and are thought to have had a strong influence on the way structure evolved in the cosmos.

The Swift spacecraft was launched in 2004.

Source: NASA

Hubble, Spitzer Collaborate for Stunning Panorama of Galactic Center

Galactic center in unprecedented detail.Credit for Hubble image: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst)


Two of the biggest space telescopes have combined forces to create a HUGE panorama of the center of the Milky Way galaxy. This sweeping, composite color panorama is the sharpest infrared picture ever made of the Galactic core. Revealed in the image are a new population of massive stars and new details of complex structures in the hot gas and dust swirling around, created by solar winds and supernova explosions. The image shows an area about 300 light-years across. Click here for options in seeing this image in small, medium or super-sized extra large resolution! Click here for a stunning movie showing the location and more detail of this image in visible light. Astronomers at the American Astronomical Society meeting pointed out the actual galactic center is in the large white region near the lower right side of the image. If you need something to keep you occupied for awhile, try counting the number of stars in this image!

More about this image…

This image provides insight into how massive stars form and influence their environment in the often violent nuclear regions of other galaxies. This view combines the sharp imaging of the Hubble Space Telescope’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) with color imagery from a previous Spitzer Space Telescope survey done with its Infrared Astronomy Camera (IRAC). The Galactic core is obscured in visible light by intervening dust clouds, but infrared light penetrates the dust. The spatial resolution of NICMOS corresponds to 0.025 light-years at the distance of the galactic core of 26,000 light-years. Hubble reveals details in objects as small as 20 times the size of our own solar system. The NICMOS images were taken between February 22 and June 5, 2008.

Source: HubbleSite